Messages

521

Show"N"Tell ( Your Machines) / Re: 9x20 Chinese Lathe Conversion

« on: March 08, 2012, 04:35:15 AM »

There was no enough room to put a substantial ball screw in place of the poor leadscrew, so I decided I to put the cross slide on linear guides to have a bit more clearance for the ball nut. On the other hand though, I didn't want to significantly reduce the clearance over the cross slide. I had very low profile Bosch Rexroth preloaded linear guides (10mm high) and I decided to you them, but also had to mill a bit into the cross slide as well as the carriage to achieve the required clearance.

Here is the carriage after milling the recess and drilling the holes for the linear blocks:


Going to mount the linear slides upside down as I figured it would be more convenient, so the carriage will have the linear blocks and guides will be mounted on the cross slide. The mounting holes for the linear blocks got counter-bored from the back:


Also, in the above photo, a lub channel has been milled into the flat sliding surface. The V-groove won't need that as it has a slightly smaller angle than 90° and there is always some clearance between the top of it and the V-guide.

On the left side, milled flat the surface for the Z ball nut assembly to be mounted.


This is the cross slide after milling the recess and drilling and tapping M3 holes for the guides:


Here's a top view, mounting holes for the X ball nut assembly have been drilled and counter-bored:


Will fill the unused holes with epoxy later.

Dan

522

Show"N"Tell ( Your Machines) / 9x20 Chinese Lathe Conversion

« on: March 07, 2012, 09:23:57 AM »

Hi,

I have this little lathe which hasn't really been used in the last couple of years, so I decided I'd better convert it to CNC which I could really use.



It is a Chinese conventional 9x20 lathe. They make them on several factories in China with different quality. This particular one was quite poorly made. The good thing in these lathes is usually their heavy cast bed and headstock and that's why it qualified as a good candidate for a conversion

Going to strip off everything and fit ball screws to both axes, with stepper motors to drive them and make up a new tray with appropriate guards. The plan is also to replace the AC induction motor driving the spindle with an AC servo motor. Quite some rework is needed to make all I want.

First, stripped off everything:


Headstock got new bearings installed and after mounting it back I checked for alignment to the Z axis:


It was found to be around 0.1mm out over 150mm. Simply filing the V-groove on the headstock in the right spots brought it to within 0.02mm over 150mm, which is a satisfactory result. It was a long process: filing a bit, mounting it back and testing and then back dismantling and filing more based on the test result. Took quite a few iterations, but it paid off

523

Show"N"Tell ( Your Machines) / Re: Just got a lathe to retrofit

« on: March 04, 2012, 04:07:24 AM »

Very well done, Hood! It's so much better than the original turret you had, which was stopping each station on its way.

Dan

524

General Mach Discussion / Re: Converting Heidenhain sine wave to TTL

« on: February 28, 2012, 12:06:37 PM »

Thanks Nosmo. will read it later.

Dan

525

General Mach Discussion / Re: Converting Heidenhain sine wave to TTL

« on: February 28, 2012, 11:22:11 AM »

If you have a link with a detailed description and some pictures, I would love to read.

Dan

526

General Mach Discussion / Re: Converting Heidenhain sine wave to TTL

« on: February 28, 2012, 11:06:42 AM »

Thanks for the information, Nosmo. That is very interesting. I didn't know that.

Dan

527

General Mach Discussion / Re: Converting Heidenhain sine wave to TTL

« on: February 28, 2012, 02:04:54 AM »

As a point of interest, all optical encoders and scales of this type, TTL included,  start off with an optically detected signal that  is sine wave in nature,

All optical encoders?! Of what type? Those I see typically have lines on the disk.

In these Heidenhain and similar scales or encoders, the arc tangent function is used to produce a high resolution absolute encoder count from the sine/cosine signal.

Don't think "absolute" is applicable to scales. In a rotary encoder I could see how they could possibly do this by matching a full sin/cos cycle to a single rotation, although I have never seen this. Usually a sine/cos encoder is just treated as an incremental encoder. I am not familiar with Heidenhain encoders in particular though.

Dan

528

Show"N"Tell ( Your Machines) / Re: Just got a lathe to retrofit

« on: February 27, 2012, 08:00:38 AM »

Yes, good indeed, Hood

The clamping and unclamping is so quiet and smooth you can hardly believe it's so powerful.

Dan

529

General Mach Discussion / Re: Converting Heidenhain sine wave to TTL

« on: February 27, 2012, 06:24:42 AM »

For what it's worth, it's not a resolver. It's rather a variation of a Sine quadrature encoder. It's implemented on a scale rather than on a rotary encoder. The sine/cosine signals are decoded in the Heidenhain controller with a AD converter of some resolution. For instance an 8-bit converter will break the sine wave into 256 parts and thus it will get a resolution multiplied by that amount compared to the scale resolution.

Considering the above, while you would be able to use a simple Schmitt trigger to produce digital quadrature signals from the sine/cosine ones, you would lose resolution to such an extent making the scale not efficient. A further electronic gearing circuit could be added, but that would make things much more complicated.

Dan

530

Show"N"Tell ( Your Machines) / Re: Coil Winder Questions

« on: February 26, 2012, 05:19:12 AM »

Hi Gary,

Machine looks fantastic! Thanks for sharing the pictures.

And I would also like to see it in action

Dan